Visible light communications refer to communicating data via the light output produced by lighting sources. Such communications is a promising way of enabling localized wireless data exchange in the future because a wide unlicensed frequency band is available for this and because light emitting diodes (LEDs) used to illuminate a room or a space can be applied to provide the communications. Possibly every lighting source of the future could become a communications source.
One visible light communications technique is based on embedding data into the light output of an illumination device by modulating the light output of the illumination device in response to a data signal (such light output is sometimes referred to as “coded light” and abbreviated as “CL”). Preferably, the light output is modulated at a high frequency and/or using a special modulation scheme so that the modulation is invisible to human beings.
For the realization of visible light communication systems of this kind, illumination systems usually employ dedicated driver electronics to allow superimposing a data signal onto the LED driving signal. FIG. 1 is a schematic illustration of such an illumination system 100. As shown, the illumination system 100 includes a dedicated driver circuit 110 and a LED 120, and is configured to generate a light output 125 according to light settings. The dedicated driver circuit 110 includes a drive signal generator 112 and a driver controller 114. The illumination system 100 is configured to operate as follows. As shown in FIG. 1, the light settings for the illumination system 100 are provided to the drive signal generator 112. The light settings indicate what the average light output 125 should be in terms, for example, of light power, e.g. defined in lumen, and color. The drive signal generator 112 translates the light settings into a drive signal (e.g., a drive current) for the LED 120 and provides the drive signal to the driver controller 114.
The driver controller 114 is further configured to receive a signal 135 from a data source 130. The signal 135 includes data bits to be embedded into the light output 125 of the LED 120. The driver controller 114 is configured to modulate the drive signal to be applied to the LED 120 in response to the signal 135 in order to embed the data bits of the signal 135 into the light output 125. Various techniques how the drive signal could be modulated in order to embed data into the light output of a light source are known to people skilled in the art (pulse width modulation, amplitude modulation, etc) and, therefore, are not described in further detail.
One problem with such an approach is that modifying a conventional LED driver to function as the dedicated driver circuit 110 described above is complicated and costly to implement. Therefore, what is needed in the art is a technique for embedding data into a light output of a LED that does not require modulating the drive signal applied to the LED.